During sleep, a muscular relaxation in the throat area occurs in humans thus causing a narrowing of the pharynx. In some individuals, this narrowing creates an airflow problem and can cause a noise called “snoring,” which can reach 90 decibels.
In certain cases, this narrowing can be so great that respiration is suspended for a certain period of time. This phenomenon of respiratory arrest is called “sleep apnea.”
There are numerous devices that prevent snoring and sleep apnea. Among the existing devices, one of the most effective is a dental device that enables the advancement of the mandible, often referred to as a mandibular protrusion device (or splint) or mandibular advancement device (or splint). This advancement of the mandible allows the opening of the pharynx to be maintained as much as possible, i.e. to minimize the narrowing thereof during muscular relaxation.
There are different types of dental appliances enabling advancement of the mandible. Some comprise two gutters, independent of one another and adapted to the top and bottom teeth respectively. These two gutters are connected by two retaining rods (often referred to as “retaining bars” or “connecting bars”). The retaining rods are fixed to the upper gutter at the canines and to the lower gutter at the first or second molars. The length of the retaining rods is chosen so that, when the device is in the mouth, the patient's jaw is kept in an advanced position.
As shown in FIG. 1, the temporomandibular articulation (TMA, or temporomandibular condyle) is a movable (or synovial) articulation that joins the mandibular fosse of the temporal bone to the condyle of the mandible by means of a fibrocartilaginous articular disc. On opening the mouth, a rotational movement of the mandibular condyle in the TMA capsule occurs. This movement is, in principle, natural and causes no pain.
As shown in FIG. 2, when the mandible in kept an advanced position, the TMA also adopts an advanced position. This advancement of the TMA can sometimes cause the patient pain.
Moreover, numerous cases of the gutters unhooking during sleep are observed. This unhooking is due to the fact that the retaining rods are positioned obliquely, in a bad position and sometimes too rigid. When the gutters unhook, the device is expelled from its protrusion position and the patient is no longer treated.
Some intraoral devices include a system for adjusting the retaining rods. However, they are usually difficult to check, i.e. it is difficult to know precisely the distance (in millimeters) of advancement of the lower jaw. Now, the advancement of the mandible (lower jaw) is the key to success for a mandibular advancement device to prevent snoring and obstructive sleep apnea. Moreover, the TMA is sensitive to each half-millimeter of advancement and each half-millimeter of advancement is very important for a patient sensitive to pain.
In order to enable the mandible to adopt an advanced position, the mandible must be open so that it can pass over all of the cusps of the upper and lower teeth. Thus, mandibular advancement devices have the effect of holding the jaw, for several hours, in an open position and of keeping the bone condyle in an advanced and unnatural position in the capsule, as shown in FIG. 2. In order to pass over all of the cusps of the upper and lower teeth, the opening of the jaw created by the devices is often from 3 to 4 millimeters and sometimes more, which is considerable. Consequently, it is important that the retaining rods connecting the gutters of the device work as far as possible in the same plane as that of the TMA.
With reference to FIG. 3, the natural occlusal plane (or occlusal plane) 20 of a patient is defined as a virtual surface that corresponds to the centric occlusion of a patient. More particularly, it is defined by the area of confrontation of the antagonist teeth, i.e. when the occlusal surfaces of the teeth of the mandible and maxilla are in contact, tangent to the incisal edges and the cusp points of the premolars and molars of each jaw. The natural occlusal plane 20 therefore respects the position of the patient's natural TMA, shown in FIG. 1.
The majority of devices are designed without considering a patient's natural occlusal plane 20. Some devices, however, are designed so that they approximately respect this plane, although there is currently no way of allowing a device to precisely respect the patient's occlusal plane. Moreover, with an approximate opening of 3 to 4 millimeters, the patient's natural occlusal plane 20 is no longer valid.